Background: Congenital hypothyroidism is one of the most frequent endocrine diseases of the newborn and requires an early diagnosis to avoid its deleterious effects on neurological and intellectual functions. Aim: To evaluate thyroid scintigraphy (TS) findings in newborns with congenital hypothyroidism (CH), detected in the national program of newborn screening, which is working in Chile since 1992. Material and methods: TS findings of 189 newborns with CH (68% female) were analyzed. Tc99m pertechnetate TS was performed at 19+/-11 days of life. The gland was classified as eutopic, ectopic or absence of contrast (AC). Eutopic glands were classified by visual and quantitative criteria as: normal, goiter and decreased contrast (DC). TS results were compared by gender and hormonal levels. Results: Forty seven percent of newborns bad ectopy, 29.1% eutopy and 24.3% AC. Eutopic gland predominated in males (44.2% vs 22.7%) and ectopy was more frequent in girls (53.1% vs 32.8%, p <0.05). Newborns with AC had the most severe hormonal alterations, without gender differences. Newborns with normal TS had less hormonal alterations than those with goiter. Conclusions: IS allows an etiological classification of CH. Thyroid dysgenesis is the most frequent cause, most of which correspond to ectopy, especially in girls. Eutopic glands are present in one third of newborns with CH. Goiter predominates, especially in males (Rev Med Chile 2003; 131: 283-9).